Start out with a posi rear end with the gears you want, I like 4.10s on a street truck with 17" and smaller rims. Next get a torque convertor in the 2800-3000 rpm stall range, hopefully smaller in diameter. While swapping the convertor, get a shift kit and billet 1-2 and 3-4 servo installed. When it comes to servos, the least you should do is the Corvette servos, they're cheap.